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Topic 7 - Weathering and Mass Wasting
Terms in this set (52)
breakdown of rocks
importance of weathering
development of landform features
weathering vs. erosion
weathering doesn't involve transport
removal of weathered material from one place to another.
transport of weathered rock.
physical characteristics of rocks i.e. colour, composition, texture...
3 main types of weathering
layer of loose, heterogeneous material covering solid rock (weathered material that has not been moved)
interface between weathered material (regolith, soil) and bedrock
physical (mechanical) weathering
- no chem rxns.
- produces small particles
- mineral alteration of decomposition
- involves chem rxn.
- new minerals can be created (i.e. secondary minerals)
- bio activities directly break down rocks (can be physical or chemical)
factors influencing the rate of weathering
- character of bedrock
- slope aspect
- vegetation cover
- surface area (fractures)
climate's control on weathering
increasing temp and precipitation generally increases weathering depth
surface area control on weathering
more fractures = more surface area = more locations for weathering to occur
character of bedrock (mineral type) control on weathering
mineral type = resistance to weathering
types of physical weathering
3. Frost action
4. Thermal expansion
Unloading (pressure release mechanism)
rocks are formed under high pressure at great depths. if the pressure is released at the surface due to erosion this causes a physical heaving off of rocks
- growth of salt crystals in rock pores typically in dry or coastal climates.
as crystal grows = the rock starts to disintegrate
Mechanisms: ice crystal growth and frost wedging.
this creates fractures which are then more susceptible to weathering.
poorly sorted, cone-shaped debris at base of steep slopes
volume change due to change in temp.
5 main types of chemical weathering
Combination with water (little chemical change)
a chemical reaction in which water reacts with a compound to produce other compounds
chemical combination of metallic minerals with oxygen
mineral dissolves, usually in water.
solution in carbonic acid.
carbonation of limestone results into karst topography
i.e. root wedging, biotic leaching, roots etc
aka mass movement
- downslope movement of soil/rock material under the influence of gravity, with the direct aid of geomorphic agents (water, wind, ice)
a strip on the land surface that is inclined.
material deposited at the base of the slope
material deposited by rivers/streams
main factors of mass wasting
resisting force of mass wasting
shear strength of rock/soil
- cohesiveness and internal friction
decreases as water content increases
driving force of mass wasting
increases with as slope increases
angle of repose
maximum angle that loose material forming a slope can maintain without slipping.
- balance between gravity and friction
a pile of sediment that is resting at the angle of repose
mass wasting occurs when the driving force (gravity) > resisting force (friction)
factor of safety
defines slope stability
Fs = (Sum of resisting forces)/(sum of driving forces)
Fs >1 stable slope
Fs< 1 unstable slope
major factors of mass wasting
- lithology, layering, structure, gradient, surface materials
- vegetation and land use
criteria for classifying mass wasting
- materials (soil/rock, coarse/fine)
- water content (dry/wet/fluid)
- rate of movement (slow/fast)
- type of movement (fall/flow)
Mass Wasting Risk
High Risk =
- saturated, igneous rock, downslope, extensive development (little veg)
rockfalls and soilfalls
occurs on very steep slopes or cliffs
- forms talus cones
translational: material moves along a planar/flat surface.
rotational (slump): moves along curved/concave surface
viscous flows occur when soil/clay/debris is liquified.
moderately rapid downslope movement of masses of saturated soil
rapid downslope flow of water and soil (mostly clays)
flow of muddy water and large amount of coarse material
SLOW downslope movement of soil due to alternate freeze thaw or wet/dry cycles
rapid soil creep
solifluction over permafrost
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